1. Field of the Invention
The present invention relates to a head liquid used to efficiently remove an ink residue and the like which adhere on a surface (hereinafter also referred to as ejection face) on which ink ejection openings of an inkjet head (hereinafter also referred to as a recording head) is formed. Moreover, the present invention relates to a method of determining the contents of components and a method of stabilizing a component ratio of the liquid as well as an inkjet recording apparatus using the liquid.
2. Description of the Related Art
A cleaning technique for a recording head which ejects an ink is a very important factor of an inkjet recording method because the method is the system in which input image data is converted to the output image using a liquid ink as a medium. Main problems in requiring the cleaning are briefly described as follows.
An ink ejection recording head directly ejects an ink through a fine nozzle (hereinafter, as such collectively referred to as an ejection opening, a liquid passage communicated therewith, and an element for generating energy utilized to eject ink unless otherwise stated) to a recording medium. Accordingly, the ejected ink hits against the recording medium and bounces back, and, in addition to the main ink involved in the recording when the ink is ejected, fine ink droplets (satellites) are ejected and drift in the atmosphere in some cases. Then, these droplets become ink mists, and, in some cases, adhere around the ink ejection opening of the recording head. Furthermore, dust drifting in the air may sometimes adhere thereto. Subsequently, the ejected main ink droplets are pulled by these attached matters, thereby the ink ejection direction is deflected, i.e., the main ink droplets are blocked from going straight in some cases.
Then, as a cleaning technique for solving this problem, an instrument called a wiping is employed to remove attached matters in the inkjet recording apparatus. The instrument wipes, at a predetermined timing, the ejection face of the recording head by means of a wiping member (wiper) made of an elastic material such as rubber.
Meanwhile, for the purpose of improving the recording density, water-resistance, light-resistance and the like of a recorded matter, an ink containing pigment components as a color material (pigment-based ink) has recently been used in many cases. The pigment-based ink is made by dispersing, in water, the color material which is originally solid by introducing a dispersant or a functional group on the surface of the pigment. Accordingly, the dried matter of the pigment ink formed by evaporating and drying the water content in the ink on the ejection face damages the ejection face seriously as compared to the dried sticky matter of a dye-based ink in which a color material itself is dissolved at a molecular level. A characteristic is also recognized that a high molecular compound used to disperse the pigment in a solvent tends to be adsorbed on the ejection face. This is a problem which occurs even in inks other than the pigment-based one in a case where a reaction liquid is added to an ink for the purpose of controlling the viscosity of the ink, improving light-resistance and for others, resulting in the presence of a high molecular compound in the ink.
To solve these problems, in Patent Documents 1 and 2, disclosed are techniques for removing an accumulated matter by applying a head liquid on the ejection face to reduce the wear of a wiper and dissolve the ink residue accumulated on the recording head in wiping the recording head. Moreover, the adhesion of a foreign matter to the recording head is prevented by forming a thin film of the head liquid on the recording head, and wiping easiness is improved by these. A construction in which the head liquid used in these wiping is stored in the body of a printer is employed.
In addition, in Patent Documents 1 and 2, disclosed are a step of cleaning by moving the wiper relative to the ejection face, and a step of supplying a nonvolatile solvent as a head liquid on the ejection face prior to the previous step. However, disclosed contents of the nonvolatile solvent are very few. Specifically, polyethylene glycol (PEG) having a molecular weight of 200 to 600 in Japanese Patent Laid-Open No. 10-138503, and polyethylene glycol having a molecular weight of 300 (PEG300) in Japanese Patent Laid-Open No. 2000-203037 are the only things that have been disclosed.
The present inventors found a problem that there were a large number of variations of the supply conditions of the solvent to the head, when a nonvolatile solvent was supplied prior to the cleaning step with the method disclosed in the above Patent Documents. When researching this problem further, the present inventors found that the causes which the nonvolatile solvent itself had were dominant. As long as the nonvolatile solvent is used by itself as the head liquid, it is usually natural that those skilled in the art select the nonvolatile solvent based on evaporation properties. Therefore, the present inventors researched processing solvents which do not tend to evaporate when the solvents are used as a head liquid. In this research process, the present inventors found that it was difficult to control the correlation between properties of the nonvolatile solvent itself and the moisture absorption property thereof attributable to the environment in which the nonvolatile solvent was placed. In addition, it was found that the nonvolatile solvent exhibited extremely large changes in weight due to moisture absorption, and thereby that the variation on the above supply amounts was not able to be reduced.
Then, the present inventors saw that the main technical problem is to stabilize the supply amount of the liquid by substantially reviewing the above liquid supplied to the ejection face to inhibit changes in weight (mass) due to the moisture absorption. When this problem was pursued, knowledge was obtained that the above problem can be solved by intentionally adding water to a nonvolatile liquid in advance. This is based on a completely reversed idea.
On the other hand, there has so far been a problem that the head liquid leaks out of the storage section due to changes in posture, vibration, and the like of the printer main body during the distribution. To be more specific, how the head liquid can be retained against leaking due to the posture, vibration, and the like during the distribution exists as an important problem to be solved. Moreover, the content of technique for inhibiting the changes in the physical properties (composition) of the head liquid due to the evaporation caused by the environmental changes during distribution and what kind of actions will be taken when drastic environmental change occurs are also important problems to be solved. The change in the physical properties (composition) of the head liquid due to the evaporation does not allow the head to sufficiently exert the cleaning effect at which the head liquid aims, thus resulting in damages to the ejection face. Furthermore, when the change in physical properties of the head liquid occurs by not only environmental change during distribution but also the change in the environment in which the printer is used, a problem occurs that the cleaning of the recording head at which an object of the head liquid aims cannot sufficiently be performed.